Carbon dioxide removal from vapor mixtures



Feb. 26, 1963 R. M. M|LTON 3,078,639

CARBON DIOXIDE REMOVAL FROM VAPOR MIXTURES Filed Jan. 19, 1960 5 Sheets-Sheet IL ZEOLITE x ADSORPTION CAPACITY For Various Temperature Ratios Temperature Ratio jl' and T in K) INVENTOR. ROBERT M. M|LTON ATTORNE) WEIGHT 7. SATURATED HYDROCARBONS ADSORBED Feb. 26, 1963 R. M. MILTON 3,078,639

CARBON DIOXIDE REMOVAL FROM VAPOR MIXTURES Filed Jan. 19, 1960 5 Sheets-Sheet 2 ZEOLITE X ADSORPTION CAPACITY For Various Temgerofure Ratios 5? 2 =3 :4 3 E 12 D D E E c l0 0 Q o '6 '5 a 1':

Temperature Ratio and T in K) [-762 INVENTOR.

' ROBERT M. MILTON ATTORNEY Feb. 26, 1963 Filed Jan. 19, 1960 5 Sheets-Sheet 3 ZEOLITE X ADSORPTION CAPACITY For Various Temperature Ratios 22 2c :8 l/ .6 .4 l2

no a 6 4 2 0 0.2 0.3 0.4 0.5 0.6 0.1 0.8 0.9 Temperature Ratio (I] and T inK) INVEN TOR. ROBERT M. MILTQN ATTORNEY Feb. 26, 1963 R. M. MILTON 3,078,539

CARBON DIOXIDE REMOVAL FROM VAPOR MIXTURES Filed Jan. 19, 1960 s Sheets-Sheet 4 ZEOLITE X ADSORPTION CAPACITY For Various Temperature Ratios WEIGHT 7, CARBON MONOXIDE ADSORBED (Grams Adsorbote/|0O grams Activated Zeolite X) 03 Temperature Ratio T, and T in K) FIG 4 INVENTOR. ROBERT M. MILTON A TTORNE).

Feb. 26, 1963 R. M. MILTON CARBON DIOXIDE REMOVAL FROM VAPOR MIXTURES Filed Jan. 19, 1960 5 Sheets-Sheet 5 ZEOLITE X ABSORPTION CAPACITY For Various Temperature Ratios m m m m Ix 26% 3 :3 265 005 398 FIG 5.

Temperature Ratio (T, and T inK) IN VEN TOR. ROBERT M. MILTON ATTORNEY United States Patent 3,078,639 7 CARBUN DIOXIDE REMOVAL FROM VAPOR MIXTURES Robert M. Milton, Buifalo, N.Y., assignor to. Union. Carbide Corporation, a corporation of New York- Filed Jan. 19, 1960, Ser. No. 3,364 8 Claims. (Cl. 5568) Thisinvention relates to' a method for adsorbing fluids and separating a mixture of fluids into its' component parts. method of separatingv carbon dioxide with adsorbents of the molecular sieve type. Still more particularly, this invention relates to a method for preferentially adsorbing carbon dioxide from a fluid mixture containing at leastone member of the group consisting of saturated aliphatic hydrocarbons containing less thanfive carbon atonis'per molecule, unsaturated hydrocarbons containing less than three carbon atoms per molecule, nitrogen, hydrogen and carbon monoxide.

This application is a continuation-in-part of my copending application Serial No. 400,386 filed' December 24', 1953, now abandoned. I

Illustrating the utility of this invention; it is'oft'en' desirable to remove carbon dioxide fromstreams containing. hydrogen, nitrogen, oxygengcarbon monoxide orair,

or mixtures of the above gases, when they are to e:

processed at low temperatures. This is because carbon dioxide would condense. as a solid material at thelow processing temperatures and thusimpair the operating efliciency of low. temperature heat exchanges. The. pref,

erential'adsorption of carbon dioxide fromsaturated'hydrocarbons may be used to. advantage in the up-grading of fuel gases, by removal of non-combustible carbon dioxide.

In the manufacture of polyethylene from ethylene in the presence of catalysts it is of great importance thattheethylene be substantially free-from carbon dioxide since the presence of even very small amounts of carbon dioxide hasa detrimental effect on the catalysts.

Broadly, the invention comprises mixing molecules, in a fluid state, of the materials to be adsorbed'or separated.

with at least partially dehydrated crystalline synthetic zeolite X. i

Zeolite X, and the methodsfor makingvzeolite Xare described. in detail and claimed'in US. patent application Serial No. 400,389 filed December 24,.1953,'.now U.S

PatentNo. 2,882,244 issued. April 14, 19,59, in the name. ofR. M. Milton. 7

It is the principal .object of. thepresent invention to. provide a process for the selective adsorption. of mole-- cules from fluids. A further object of the invention is to i provide a method. whereby certain molecules. may: be;

adsorbed and separated 'by crystalline synthetic zeolite X.

Inthe drawing,

FIGURE v1 is a graph showing the weight=percent of. carbondioxide adsorbed versus the temperature ratio T T for zeolite X.

FIGURE 2 is a graph showing the weight percentofsaturated hydrocarbons adsorbed versus thetemperature' ratio T /T forzeolite X.

FIGURE 3 is a graph showing the weight percent of More particularly, the invention relates to a Patented. Feb. 26, 1963 nitrogen adsorbed versus the temperature ratio T l'T- for zeolite X. i i

FIGURE 4 is a graph showing the weight percent; of carbon monoxide'adsorbed versus the temperature ratio T-,; /T forzeolite X- FIGURE.- 5 is a graph showing theweight percent-of}- unsaturated hydrocarbons adsorbed versus the tempera tu-re ratio 13/ T forzeolite X.-

The formula for zeolite X may be written as follows? In; this formula Mi "represents ametal, n its valence.. and Y may be any value up 'to, 8- dependingon the identity of the metal and the'degree' of dehydration of the crystals. X-ray diffraction data may be employed to'define the crystal structure ofzeolite X. Such'informati-on andprocessesifor synthesizing zeolite X are provided" in' UI S Patent 2,882,244;

Tlie adsorbents" contemplated herein include not i only. the sodium form ofzeolite X, which is'a'common form produced but also-crystalline material's obtained from such'a'zeolite by partialorcomplete replacement of the sodiumion-with other cations. The'so'dium' cations can bereplaced, inpart'or entirely by ion exchange with other monovalent, divalent or trivalent cations. This maybe accomplished by io exchange. techniques.

The'following data contained in'lable I shows zeolite X adsofrption ofjcarbon dioxide, saturated aliphatic hydrocarbon's containing less than five carbon atoms per molecule, unsaturated hydrocarbons containing less-thanthree carbon atoms per molecule andloww boiling point gases,vnitrogen,'hydrogen and carbon monoxide. Inthistable; as elsewhere in the'specification, the term -weight percent adsorbed refers to'the percentage increase in the weight'of'the adsorbent. I TABLE I Temperature; 0.

Weight Percent Adsorbed Pressure,

Adsorbentmm; Hg.

- Adsorbatel t to ke r NNNNINHOM ica mocadcnayqmcnmc n: 3 Nb- BOIHOSMOIOWOUIOWL TABLE I-Continued Weight Percent Adsorbed Tempera- Pressure Adsorbent Adsorbate ture, 0. mm. Hg:

160 100 less th 100 less th 500 less til Another unique property of zeolite X is its strong preference for polarizable molecules, providing of course, that these molecules are of a size and shape which permits them to enter the pore system. This is in contrast to charcoal and silica gel which show a main preference based on the volatility of the adsorbate. The following table shows the adsorption of carbon dioxide,a polarizable molecule, on charcoal, silica gel and sodium zeolite X.

Wei ht ercent Ads b d Adsorbate Tempera- Pressure g p m e ture (mm.Hg) C.) NagX Silica Charcoal Gel Carbon Dioxide 25 50 15. 7 1. 3 2. 2

An illustration of the ailinity of zeolite X for ethane, ethylene and propane is presented below.

Weight percent Ad- Ternperasorbed on NazX Pressure (mm. Hg) ure CaHa The adsorptive selectivityof zeolite X for carbon monoxide, a polar molecule is illustrated below.

Temperawdght Pressure percent Adsorbate E g (mm. Hg) Adsorbed on PaX Carbon Monoxide 75 500 10.0

An important characteristic of zeolite X is its property of adsorbing large amounts of adsorbates at low adsorbate pressures, partial pressures or concentrations. This property makes zeolite X useful in the removal of adsorbable impurities from gas mixtures since it has a relatively high adsorption capacity even when the material being adsorbed from a mixture is present in very low concentrations. Eflicient recovery of minor components of mixtures is also possible. The high adsorption at low pressures on zeolite X are illustrated in the above Table I.

These data of Table I show that carbon dioxide is mor strongly adsorbed than any other of the tabulated materials at comparable temperatures and pressures and illustrate several possible reparations by means of zeolite X. For example, zeolite X can be used for the selective adsorption of carbon dioxide from fluid mixtures containing both carbon dioxide and saturated aliphatic hydrocarbons.

The table also shows that at the same temperature (25 C. in the table) carbon dioxide is more strongly adsorbed at a given pressure than are nitrogen, hydrogen and carbon monoxide. Thus, carbon dioxide may be removed from mixtures with these less strongly adsorbed gases by means of zeolite X.

Likewise, Table I shows that carbon dioxide is more strongly adsorbed than ethylene so that carbon dioxide may be readily removed from ethylene mixtures through the use of zeolite X.

An advantage that may be taken of this high adsorption of zeolite X at low pressures is the operation of adsorption processes at higher temperatures than are normally used with common adsorbents. The adsorptive power of physical adsorbents usually decreases with increasing temperature, and therefore while the adsorption capacity of many adsorbents in a certain separation may be sufficient it operated at one temperature, the capacity may not be sufiicient to make operation feasible at a higher temperature. With strongly adsorbing zeolite X, however, substantial capacity is retained at higher temperatures.

, Zeolite X may be used as an adsorbent for the purposes indicated above in any suitable form. For example, a column of powdered crystalline material has given excellent results as has a pelleted form obtained by pressing into pellets a mixture of zeolite X and a suitable binding agent such as clay.

The present process for separating carbon dioxide from certain vapor mixtures depends upon interrelated properties of zeolite X with respect to the adsorbed phase. The first property is the selectivity of the internal surfaces of the crystal towards this strongly polarizable compound as compared to saturated aliphatic hydrocarbons, unsaturated hydrocarbons, nitrogen, hydrogen and carbon monoxide. As previously discussed and illustrated by Table I, zeolite X is capable of adsorbing all of these constituents based on a consideration of the zeolite X pore size and critical molecular dimensions of the compounds. For example, the pores of zeolite X are sufiiciently large and in fact do receive methane, pentane, ethylene, nitrogen, hydrogen and carbon monoxide.

Based on these considerations, one skilled in the art would logically conclude that zeolite X would not possess any particular selectivity for carbon dioxide in preference to the other constituents of the present vapor mixture. Contrary to these expectations, it has been discovered that zeolite X possesses an extremely strong selectivity for carbon dioxide to the substantial exclusion of saturated and unsaturated aliphatic hydrocarbons, hyd'rogen, nitrogen and carbon monoxide. One reason for this selectivity is the highly polarizable nature of carbon dioxide as compared with the other possible constituents of the vapor mixture.

A second interrelated property is the relationship of the boiling point or vapor tension characteristics of an individual fluid or clearly related type of fluid to the capacity of the crystalline zeolite X to adsorb carbon dioxide at a given temperature and pressure. More specifically it has been discovered that a relationship exists between the amount of carbon dioxide adsorbed by zeolite X, and the temperature ratio T T where T is the temperature in degrees Kelvin at which the adsorption 5. iscarried out, assuming that the temperature of the fluid and the adsorbent are in equilibrium. T is the temperature in degrees Kelvin at which the vapor pressure of the fluid is-equal to the partial pressure or vapor tension of the fluid in equilibrium with the zeolite adsorbent. Stated in another way, T isthe temperature at which the vapor pressure of the adsorbate is equal to the partial pressure ofthe adsorbate during adsorption. T is actually the dew point determined at the adsorption conditions.

Thisrelationshipis clearly shown in FIG. 1 which is a plot of theweight percent of carbon dioxide adsorbed versus. the temperature ratio T /T for zeolite X. Table II is a summary of the data from which FIG. 1 was pre-. pared, the data for the first five examples having been assembled from tests. described in more detail in other parts, of the specification. That is, the T values for these examples were. obtained from the preceding portion of the specification. TheT values were read from thevapo-r pressure tables in Industrial and Engineering Chemistry, vol. 39, page 517, April 1947.

The plots of FIGS. 2, 3, 4. and 5 are. presented to il-' lustrate in conjunction with FIG. 1 the preferential adsorption of carbon dioxide which is obtained through the use of zeolite X.

TABLE II Pressure Weight T T Adsorbate (mm. Percent K. K. T2/T1 Hg) Adsorbed CO2 0.1 2. 7 298 126 0.42 1. 6 3. 7 298v 1 1 0.47 80 18. 0, 298 171 0.58 750 26. 3 298 194 0.65 50 15. 7' 8 166 0.56 4 6. 3 298 147 0.50 9 298 154 0.52 25 12. 5 298 150 0.54 30 35. 6 195 162 0.- 83 8 31. 2 195 152 0.78

An inspection of Table II will reveal that it includes carbon dioxide adsorption at temperatures from 78 C. to 25 C. and adsorbate pressures from 0.1 mm. Hg to 750 mm. Hg. The present invention utilizes this temperature ratio relationship in combination with the previously discussed polarizable compound selectivity property of zeolite X with respect to carbon dioxide to provide a novel separation process.

The present invention combines the previously discussed properties of zeolite X in such a manner that a novel process is provided for separating carbon dioxide from a vapor mixture containing at least onemember of the group consisting of saturated aliphatic hydrocarbons containing less than five carbon atoms per molecule, unsaturated hydrocarbons containing less than three carbon atoms per molecule, hydrogen, nitrogen and carbon monoxide. In its broadest form, the process consists of contacting the vapor mixture with a bed of at least partially dehydrated crystalline zeolite X adsorbent material. The carbon dioxide depleted vapor mixture is then discharged from the crystalline zeolite X bed. Such contact is preferably effected under conditions such that the temperature ratio T T with respect to the inlet end of the bed and with respect to the carbon dioxide of the vapor mixture is between 0.43 and 1.0, where T is the adsorption temperature and is less than 973 K., and T is the temperature at which the carbon dioxide has a vapor pressure equal to its partial pressure in the vapor mixture. The lower limit of 0.43 for the temperature ratio T /T is fixed by the discovery that below this value there is a smaller percentage change in adsorption capacity per unit change in the temperature ratio. In contrast, above 0.43 there is a larger percentage change in adsorption capacity per unit change in the temperature ratio. Stated in another way, if it is desired to obtain a certain incremental adsorbate loading at a specified adsorption-temperature with a given feed stream, it would benecessary to increase thepressure of operation by a greater percent if the temperature ratio is below 0.43 than if it is maintained above this value in accordance with the invention. Also, the temperature ratio of 0.43 corresponds to a bed loading of about 2.5 weight percent-adsorbate and if the temperature ratio were reduced below this value, a larger adsorption bed would be required with its attendant higher investment and operating expenses.

The upper limit of 1.0 for the temperature ratio should not'be exceeded, because if the adsorption temperature is equal to or less than the dew point, condensation of the carbon dioxide will occur, thereby essentially eliminating the sieving action of the zeolite X adsorbent. The broad upper limit of 973 K. for T is due to the fact that above this temperature, the crystal structure of zeolite X will be disrupted or damaged with consequent loss of adsorption capacity and reduction in pore size, thereby fundamentally changing its adsorptive characteristics.

For carbon dioxide adsorption from a mixture containing saturated hydrocarbon, the present process is most efliciently performed if T the adsorption temperature is less than 644 K. but higher than 233 K. This is for the reason that above such range, the saturated hydrocarbon in contact with zeolite X will tend to crack, isomerize, aromatize and polymerize, all of which will clog the pores and cause loss of capacity of the zeolite X molecular sieve. Below 233 K. relatively economical refrigerants such as Freon-l2 cannot be employed, thereby necessitating more expensive refrigerating systems. Also, the mechanical properties of metals deteriorate rapidly below about 233 K., so that special construction materials must be employed for adsorbers operating'in this low temperature range. The increase in zeolite X adsorptive capacity for carbon dioxide at reduced temperatures justifies the employment of refrigeration down to the 233 K. level. Furthermore, for maximum efficiency, T is preferably below 304 K. which is the critical temperature of carbon dioxide. This is'to more effectively utilize the adsorptive capacity of zeolite- X;

In the adsorption of carbon dioxide from a mixture containing unsaturated hydrocarbons containing less than three carbon atoms per molecule, the present process is most eificiently performed if T; is lessthan 533=K. but higher than 233 K. Above this range thehydrocarbon willtend to isomerize, crack, aromatize and polymerize, all of which will clog the pores and cause'loss of capacity of the zeolite X molecular sieve. Also, for maximum efliciency, T is preferably below 304 K., the critical temperature of carbon dioxide.

The present invention-also contemplates a process-for continuously separating carbon dioxide from a vapor mixture containing at least one member of the group consisting of saturated aliphatic hydrocarbons containing lessthan five carbon atoms per molecule, unsaturated hydrocarbons containing less than three carbon atoms permolecule, hydrogen, nitrogen and carbon monoxide. Thiscontinuous process includes two steps, an adsorptionstroke'and a regeneration stroke. The adsorption stroke: is the sameas'the previously described adsorption where-- the temperature ratio T T 1 is between, 0.43 and 1.0; and the broad range for T is less than 973 K. In the re generation stroke, at least part of the adsorbed carbon dioxide. is removed bysubjecting the zeolite X adsorbent to conditions such that the temperature ratio Tg/T atthe endofthe'regeneration stroke with respect to the carbon dioxide is less than the temperature. ratio at .the' end of the adsorption stroke. Also, the difference in total adsorbate loading between the ends of the adsorp-J tionand regeneration strokes is at least 0.5 weight per cent for increased efiiciency. of the overall continuous process. A lower dilferential adsorbate loading would entail prohibitively large adsorber units. During the regeneration stroke, T is the regeneration temperature and is less than 973' K. for the broad range and T is the temperature. at which the. carbon v, dioxide has a vapor pressure equal to its partial pressure over the zeolite X bed at the end of the regeneration. It will be understood by those skilled in the art that at least two adsorbent beds may be provided, with one bed on adsorption stroke and the other bed on regeneration stroke. The respective flows are then periodically switched when the first bed becomes loaded with the adsorbate so that the latter is placed on regeneration stroke and the second bed is placed on-stream.

For carbon dioxide adsorption from mixtures containing saturated hydrocarbons, the continuous process is most efficiently performed if T the adsorption temperature, is less than 644 K. but higher than 233 K. for previously stated reasons. Also, for maximum efliciency during the adsorption stroke, T is below 304 K., the critical temperature of carbon dioxide. During the regeneration stroke, T is preferably below 644 K. and above 233 K., also for the previously discussed reasons.

For carbon dioxide adsorption from a mixture containing unsaturated hydrocarbons, the continuous process is most efficiently performed if T is less than 533 K. but higher than 233 K. for previously stated reasons. Also for maximum efiiciency during the adsorption stoke, T is below 304 K. During the regeneration stroke, T is preferably below 533 K. and above 233 K., also for the previously discussed reasons.

Finally, the diiference in total carbon dioxide loadings between the ends of the adsorption and regeneration strokes is preferably at least 1.0 weight percent for increased efiiciency of the overall process.

It will be understood by those skilled in the art that the temperature ratio may be adjusted by well-known methods, as for example, heating the bed by direct or indirect heat transfer, employing a purge gas, or by drawing a vacuum on the bed during the regeneration stroke. Also, during the regeneration stroke, the ratio may be adjusted for favorable operation by varying either or both the temperature and the pressure.

The many advantages of the invention are illustrated by the following examples:

Example I A vapor mixture is provided containing 0.1 mole fraction carbon dioxide, the remainder being methane, at a total pressure of 100 p.s.i.a. The mixture is to be contacted with a bed of zeolite X at a temperature of 25 C. The zeolite bed is to be regenerated for continuous operation.

The potential capacity of the bed to adsorb carbon dioxide at the bed inlet section may be determined as follows: Since the partial pressure of carbon dioxide is p.s.i.a., T will be 189 K., as read from the previously referenced vapor pressure table. Accordingly, T T will be l89/298=0.64. This temperature ratio will provide a loading of 25 weight percent of carbon dioxide on the zeolite X adsorbent as determined by a reading of the FIG. 1 graph. The potential capacity of the adsorbent bed inlet end for methane may be determined in a similar manner by reference to FIG. 2. For methane, T is 139 K. and T /T 1 is equal to 0.47 which will provide a load ing of 0.6 weight percent. The adsorption may be terminated when traces of carbon dioxide first appear in the effiuent if complete elimination of carbon dioxide from the effluent is desired.

During the regeneration stroke, the bed temperature is kept at 453 K. and the pressure is reduced to 14.7 p.s.i.a. corresponding to a T value of 195 K. with respect to carbon dioxide. Under these conditions, the T /T ratio will be 0.43 and the residual loading of carbon dioxide will be reduced to about 2.5 weight percent.

Example II A vapor mixture is provided containing 0.04 mole fraction carbon dioxide, the remainder being ethylene, at a total pressure of 200 p.s.i.a. The mixture is to be contacted with a bed of zeolite X at 25 C. The zeolite bed is to be regenerated by heating the feed stream and passing it therethrough as a purge gas. Under these conditions, the potential capacity of the bed to adsorb carbon dioxide and ethylene may be determined in the same manner as described previously in conjunction with Example I. That is, for carbon dioxide at the bed inlet section, T will be 187 K. so that the temperature ratio T /T is 0.63 which corresponds to a loading of 24 weight percent carbon dioxide on the adsorbent as read from FIG. 1. The potential capacity of the adsorbent bed at the inlet end for ethylene may be determined in a similar manner by reference to FIG. 5 to give a loading for ethylene of about 18.8 weight percent. The adsorption stroke, may be terminated when traces of carbon dioxide first appear in the efiluent if complete elimination of carbon dioxide from the efiluent is desired.

Assuming a desired residual carbon dioxide loading of about 2.5 weight percent, regeneration of the zeolite X used in Example II can be readily achieved by employing the feed gas as a purging medium, and heating the bed and/ or such gas to provide a regeneration temperature of 435 K. (162 C.). This temperature is based on a T /T value of 0.43 as read from FIG. 1 at a loading of about 2.5 weight percent and a T of 187 K.

Alternatively, if regeneration is to be effected by drawing a vacuum pressure of 50 mm. Hg on the bed, T would be 166 K. This temperature corresponds to the vapor pressure of carbon dioxide at 50 mm. Hg as read from the previously referenced table. Since the residual carbon dioxide loading is to be about 2.5 weight percent, T /T will be 0.43 as read from FIG. 1. With this value for the temperature ratio, the required T is 386 K.

When the inlet vapor mixture contains nitrogen or carbon monoxide, the potential capacity of the zeolite X adsorbent for these constituents is similarly determined by reference to the vapor pressure tables and FIGS. 3 and 4, respectively. Also, if hydrogen is present, the potential capacity of zeolite X may be determined in an analogous manner.

Although the preferred embodiments have been described in detail, it is contemplated that modifications of the process may be made and that some features may be employed without others, all within the spirit and scope of the invention as set forth herein.

What is claimed is:

1. A process for separating carbon dioxide from a vapor mixture containing carbon dioxide and methane, which comprises contacting said vapor mixture with a bed of at least partially dehydrated crystalline zeolite X adsorbent material and thereafter discharging the carbon dioxide depleted vapor stream from said bed.

2. A process for separating carbon dioxide from a vapor mlxture containing carbon dioxide and ethane, which comprises contacting said vapor mixture with a bed of at least partially dehydrated crystalline zeolite X adsorbent material and thereafter discharging the carbon dioxide depleted vapor stream from said bed.

3. A process for separating carbon dioxide from a vapor m'xing containing carbon dioxide and propane, which comprises contacting said vapor mixture with a bed of at least partially dehydrated crystalline zeolite X adsorbent material and thereafter discharging the carbon dioxide depleted vapor stream from said bed.

4. A process for separating carbon dioxide from a vapor mixture containing carbon d'oxide and butane, which comprises contacting said vapor mixture with a bed of at least partially dehydrated crystalline zeolite X adsorbent material and thereafter discharging the carbon dioxide depleted vapor stream from said bed.

5. A process for separating carbon diox'de from a vapor mixture containing carbon dioxide and ethylene, which comprises contacting said vapor mixture with a bed of at least partially dehydrated crystalline zeolite X adaoraeae sorbent material and thereafter discharging the carbon dioxide depleted vapor stream from said bed.

6. A process for separating carbon dioxide from a vapor mixture containing carbon dioxide and hydrogen, which comprises contacting said vapor mixture with a bed of at least partially dehydrated crystalline zeolite X adsorbent material and thereafter discharg'ng the carbon dioxide depleted vapor stream from said bed.

7. A process for separating carbon dioxide from a vapor mixture containing carbon dioxide and nitrogen, which comprises contacting said vapor mixture with a bed of at least partially dehydrated crystalline zeolite X adsorbent material and thereafter discharging the carbon dioxide depleted vapor stream from said bed.

8. A process for separating carbon dioxide from a vapor mixture containing carbon dioxide and carbon monoxide, which comprises contacting said vapor mixture with a bed of at least partially dehydrated crystalline zeolite X adsorbent material and thereafter discharging the carbon dioxide depleted vapor stream from said bed.

References Qited in the file of this patent Separation of Mixtures Using Zeolites as Molecular Sieves. Part I. Three Classes of Molecular-Sieve Zeolite by R. M. Barrer, J. Soc. Chem. Ind, vol. 64, May 1945.

Examine These Ways To Use Selective Adsorption, Petroleum Refiner, vol. 36, No. 7, July 1957, pages 136- 140. 

1. A PROCESS FOR SEPARATING CARBON DOIXIDE FROM A VAPOR MIXTURE CONTAINING CARBON DIOXIDE AND METHANE, WHICH COMPRISES CONTACTING SAID VAPOR MIXTURE WITH A BED OF AT LEAST PARTIALLY DEHYDRATED CRYSTALLINE ZEOLITE X 